/ɪnˈtɜrnəl si/ – Phrase
Definition: nội hải.
A more thorough explanation: An internal sea is a body of water that is partially enclosed by land, with a narrow outlet to the open ocean. It is considered to be part of the territory of the country that surrounds it, and is subject to the jurisdiction and control of that country.
Example: The United Nations Convention on the Law of the Sea establishes the legal framework for the rights and responsibilities of countries bordering an internal sea.